Studies on Caisson Type Breakwater – A Physical and Numerical Approach

Abstract

The design and construction of coastal structures such as breakwaters, at greater water depths is rapidly increasing as a result of the increasing draught of large vessels and off-shore land reclamations. Vertical caisson-type breakwaters may be the best alternative compared to ordinary rubble mound breakwaters in larger water depths, in terms of performance, total costs, environmental aspects, construction time and maintenance. To fulfil the functional utility and impact of the structure on the sea environment, it is necessary to study the hydraulic performance of such breakwaters. In the present project, the hydrodynamic performance of caisson breakwater with various geometric configurations are studied in detail. In the first phase, a physical model approach is carried out extensively to study the stability of toe protection for vertical caisson breakwater. The determination of the size of the toe armour units and their cross-section for the stable design are investigated. The applicability of the Brebner and Donnelly (Coast Eng Proc 1: 24, 1962) design curve for depth-limited conditions is validated for a certain fixed relative foundation depth (d1/d). In the second phase, an investigation of the non-perforated caisson type breakwater is performed considering different wave conditions. The variation of dynamic wave pressure, wave force, wave run-up, and wave reflection are determined for this structure. The maximum wave force on the caisson breakwater is calculated from measured pressure values and is compared with the wave forces calculated by Goda’s and Sainflou wave theories. The comparison of results illustrate that the Goda’s formula provides a good estimation of wave force distribution compared with the experimental findings. In the third phase, a numerical model of caisson breakwater is developed to study its performance using the computational fluid dynamics (CFD) approach using Ansys- Fluent and validated the same using experimental data. In the fourth phase, the experimental investigations are carried out on non-perforated vertical wall breakwater with the presence of a vertical and horizontal slotted barrier. In the fifth phase, the perforations (i.e 8 %, 10%, 13%, 15%, 20%) are introduced in the front face of the caisson breakwater to analyse the hydraulic performance to arrive at better perforations in reducing the wave forces, wave reflection and wave runup.